A critical security vulnerability has been identified in Realtek’s RTL8762E SDK v1.4.0, which allows attackers to exploit the Bluetooth Low Energy (BLE) Secure Connections pairing process to launch denial-of-service (DoS) attacks. This flaw, discovered in the RTL8762EKF-EVB development platform, arises from improper validation of protocol state transitions during the pairing sequence.
Understanding the Vulnerability
The BLE Secure Connections pairing process is designed to establish a secure link between devices by exchanging cryptographic keys. According to the Bluetooth Core Specification v5.3, this process requires strict message ordering, where the Pairing Random message must only be sent after the successful exchange of Pairing Public Keys. However, the affected Realtek SDK fails to enforce this critical sequencing requirement.
The root cause lies in insufficient state validation within the Security Manager Protocol (SMP) layer. The BLE stack processes incoming Pairing Random packets without verifying that the public key exchange phase has been completed, violating the expected state machine transitions defined in the Bluetooth specification. This implementation oversight allows the device to accept premature Pairing Random packets, triggering undefined internal states that compromise the pairing process integrity.
Exploitation and Impact
Exploitation of this vulnerability is straightforward and requires no special privileges or authentication. An attacker can establish initial BLE communication with the vulnerable device and send a crafted Pairing Random packet prematurely. This out-of-sequence packet disrupts the state machine, leading to a failure in the pairing process and effectively blocking secure BLE connections.
The impact of such an attack is significant, as it can prevent legitimate devices from establishing secure connections, thereby disrupting normal operations. This is particularly concerning for embedded systems and IoT devices that rely on BLE for secure communication.
Remediation Strategies
To mitigate this vulnerability, it is essential to implement comprehensive state validation within the SMP layer to ensure strict adherence to protocol specifications. Developers should modify the BLE stack to discard any messages received out of sequence according to the SMP state machine requirements, specifically ensuring Pairing Random packets are only accepted after both sides have successfully exchanged Pairing Public Keys.
Organizations using affected Realtek SDK versions should apply patches or updates provided by Realtek to address this issue. Additionally, developers should review their BLE implementation to ensure compliance with the Bluetooth Core Specification and prevent similar vulnerabilities.
Conclusion
The discovery of this vulnerability underscores the importance of rigorous protocol implementation and validation in secure communication systems. By adhering to established specifications and conducting thorough testing, developers can prevent such flaws and enhance the security of their products.
